1) There is a G5 Music label which has uploaded an EP of a hip hip artist on Last.fm. Probably this is the same as the G5 Music page on Facebook, see sources.
2) G5 the Jett is a hip hop artist from Oakland.
3) G5 Clive is a hip hop artist from Washington.
4) The G5 Project is a Japanese band.
5) For the Spanish flamenco group see G-5.